The popularity of small hand, wristwatch and pen sized calculators has increased in recent years due to their portability. One of the most severe problems in miniaturizing such calculators has been the requirement for a plurality of push-button or input devices which can be conveniently used and maintained, and still provide rapid and reliable operation. Various attempts have been made to decrease the number and configuration of input buttons or keys, with the apparent minimum required being reduced to three or four, see U.S. Pat. No. 4,120,040 and U.S. Pat. No. 4,086,654. The past minimum number of four buttons is used to perform only the simplest arithmetic functions--addition, subtraction, multiplication and division. Other devices of interest employ a bezel type input (e.g., U.S. Pat. No. 4,019,037) or a rotary input (e.g. U.S. Pat. No. 4,044,242), or combination rotary input with a sliding integer scale (e.g. U.S. Pat. No. 4,007,364), or multiple input keys. These devices have proven to be complicated, slow and unwieldy, and require numerous parts.